The invention relates to a method for converting an alcohol into a motor fuel mixture and also to an apparatus for practicing the method.
Replacing conventional fossil motor fuels by alternative motor fuels is gaining more and more attention. Notably alcohols, such as methanol or ethanol, are attractive in this connection, since they are obtainable from regenerative sources in a relatively simple way. However, owing to their low cetane number, these motor fuels cannot be used in auto-ignition, diesel engines. To facilitate combustion in diesel engines, these motor fuels can be additized with additives, such as dimethyl ether or diethyl ether, for raising the cetane number.
A mixture of alcohol, ether and water can also be produced directly during the operation of a combustion engine, in an upstream process, from an alcohol, for example from methanol or ethanol, by using a suitable catalyst.
U.S. Pat. No. 4,422,412 A discloses a method for converting an alcohol into a motor fuel mixture wherein the alcohol (methanol for example) which has been heated to a suitable reaction temperature is converted by means of a catalyst in a reactor into a motor fuel mixture in accordance with the accompanying reaction equation:2CH3OH⇄CH3—O—CH3+H2O  reaction 1
The methanol (CH3OH) used here is thus converted in the reactor to form additionally dimethyl ether (CH3—O—CH3) and water (H2O). When ethanol is used for the conversion method to produce the motor fuel mixture, a mixture of ethanol, diethyl ether and water can be produced using the reactor. Gamma-Aluminumoxide can be used as catalyst in the reactor.
The motor fuel mixture obtained according to this known method tends to vary greatly in quality, as evidenced by a greatly varying water content, and therefore in practice it cannot be used to run diesel engines. The variations in quality which occur lead to greatly varying cetane numbers and consequently to greatly varying igniting timing. Moreover, the motor fuel mixture obtained is not always equally suitable for all engine operating points.